Green’s Dictionary of Slang

Quaker oat n.

a coat.

1932		‘P.P.’ Rhy. Sl.
1937		L. Lane Me and My Girl I iii: bill: Quaker oat. charles: Porridge, sir? bill: Naow! Coat.
1960		J. Franklyn Dict. of Rhy. Sl.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1999		R. Walton ‘Cockney Jack and the Beanstalk’ 🌐 A little wrinkled heavenly plan with a funny pointed barrel of fat and funny pointed ones and twos and a dirty Quaker oat stepped out into the frog and toad.